1. Field of the Invention
The present invention relates to a paper feed apparatus, and more particularly to a bottom-drawing-type paper feed apparatus which is suitable for, for example, an image scanner and which has an improved sheet separation performance, eliminates necessity of a pre-operation before setting of sheets of paper to thereby facilitate operation, and prevents occurrence of a paper jam and/or upturn of a leading end of a sheet.
2. Description of the Related Art
In general, an image scanner is provided with an automatic paper feed apparatus which enables the image scanner to automatically transport and read a huge amount of documents. Such an automatic paper feed apparatus comprises a picking mechanism for transporting a plurality of sheets of paper stacked on a shooter to a predetermined standby position; a separation mechanism for drawing inside a sheet of paper at a time from the standby position; a feed mechanism for feeding the separated sheet; and a discharge mechanism for discharging the sheet to a stacker or the outside of the scanner after the sheet has been scanned. Recently, such an automatic paper feed apparatus has been controlled by means of a microprocessor.
FIG. 13 is an explanatory view showing a main portion of a conventional paper feed apparatus. As shown in FIG. 13, a picking roller 72 and a separation roller 73 are drivingly linked via a gear 83 so that the picking roller 72 and the separation roller 73 rotate in the same direction; and the separation roller 73 is drivingly linked to a feed roller 74 via a gear 79. Further, a pressing arm 81 is disposed in sliding contact with the picking roller 72, and a separation pad 80 is disposed in sliding contact with the separation roller 73. Moreover, a gate 84 is disposed on a paper feed path between the picking roller 72 and the separation roller 73.
The pressing arm 81 is provided in order to enable reliable transport of sheets of paper set on a shooter 71 and is formed from a spring member. One end of the pressing arm 81 is fixed to an unillustrated frame, and the other end of the pressing arm 81 is biased toward the picking roller 72 to thereby come into contact with the top sheet of paper while applying a certain pressing force to the sheets of paper. By means of frictional force which is generated between the picking roller 72 and the sheets of paper due to the pressing force, the sheets of paper are transported from the shooter 71 to the separation roller 73.
The gate 84 is provided so as to secure a clearance in the thickness direction of sheets on the paper feed path in order to enable passage of a few sheets of paper, thereby enabling reliable transport of the sheets. The gate 84 has a paper-abutting surface which forms an acute angle with respect to the paper transport direction along the paper feed path.
A one-way clutch is attached to each of the picking roller 72, the separation roller 73, and the discharge roller 75 such that the separation roller 73 rotates in the counterclockwise direction in FIG. 13, and the discharge roller 75 rotates in the clockwise direction (paper transport direction) only. Further, a sensor 82 for detecting the leading end of each sheet of paper is disposed along the paper feed path in the vicinity of and on the downstream side of the separation roller 73. Further, a sensor 85 for detecting the leading and trailing ends of each sheet of paper is disposed along the paper feed path in the vicinity of and on the downstream side of the feed roller 74.
In the above-described automatic paper feed apparatus, when a pulley 76 connected to an unillustrated motor is rotated in the counterclockwise direction, a belt 77 engaged with the pulley 76 causes the feed roller 74 to rotate in the counterclockwise direction, or in a direction opposite the paper transport direction. At this time, the discharge roller 75 does not rotate even when the belt 77 moves. Meanwhile, the picking roller 72 and the separation roller 73 are rotated in the counterclockwise direction (paper transport direction) via gears 79 and 83. Therefore, a single sheet of paper is drawn inside from the unillustrated paper stack on the shooter 71 by the picking roller 72 and is transported toward the separation roller 73. If a plurality of sheets of paper are picked erroneously, the gate 84 and the separation pad 80 prevent transfer of the plurality of sheets, so that only a single sheet of paper in close contact with the picking roller 72 and the separation roller 73 is transported toward the feed roller 74. Therefore, transportation of two sheets (double feed or a like) problem does not occur.
Even when the leading end of the transported sheet of paper reaches the feed roller 74, the sheet of paper is not supplied to the feed roller 74 instantaneously but is stopped there for a short period of time, because the feed roller 74 is rotating in the counterclockwise direction, which is opposite the paper transport direction. During this period, positioning of the leading end of the sheet is performed. The stop time is controlled on the basis of a predetermined number of pulses or a predetermined period of time after the sensor 82 detects the leading end of a sheet of paper. After elapse of the predetermined period of time, the unillustrated motor rotates in the reverse direction in order to rotate the pulley 76 in the clockwise direction. Therefore, the feed roller 74 and the discharge roller 75 are also rotated in the clockwise direction via the belt 77. As a result, the sheet of paper is transported by the feed roller 74 to a reading mechanism 78. Immediately before the leading end of the sheet of paper reaches the reading mechanism 78, the leading end is detected by the sensor 85. In response to a detection signal generated by the sensor 85, the read operation is started. When the sensor 85 detects the trailing end of the sheet of paper, the read operation is ended, and the discharge roller 75 is operated to discharge the sheet of paper onto an unillustrated stacker.
In the above-described automatic paper feed apparatus, when, as shown in FIG. 14A, a large number of sheets of paper 90 are placed onto the shooter 71, the sheets of paper 90 must be aligned in a staggered manner beforehand such that the leading ends of the sheets of paper 90 form a knife-edge-like shape 91, as shown in FIG. 14B, in order to make it easy to feeding the sheets of paper to the separation roller 73.
The above-described conventional paper feed apparatus has the following drawbacks.
Since the gatexe2x80x94which forms a clearance in the thickness direction of sheets of paper on the paper feed pathxe2x80x94extends at an acute angle with respect to the paper transport direction, a vertical component force is generated and is applied to the sheets of paper, resulting in an impairment in paper separation performance.
Further, when a large number of sheets of paper are placed onto the shooter, the sheets of paper must be aligned in a staggered manner beforehand such that the leading ends of the sheets of paper form a knife-edge-like shape. However, this pre-operation is considerably cumbersome, and is sometimes neglected or forgotten. In this case, sheets of paper cannot be supplied smoothly.
Moreover, the separation roller is disposed between the picking roller and the feed roller; the pressing arm is disposed in sliding contact with the picking roller; and the separation pad is disposed in sliding contact with the separation roller. Therefore, the transport mechanism portion of the paper feed apparatus has a relatively large size.
Further, since the picking roller is disposed such that a portion of the outer circumference of the picking roller is exposed to the outside from an opening provided in a paper guide, when the picking roller picks and transfers a sheet of paper, the sheet may be caught between the picking roller and the paper guide, resulting in occurrence of a paper jam and stoppage of paper feed.
Moreover, although the separation pad is disposed to prevent so-called double feed in which a plurality of sheets of paper are supplied, the disposition of the separation pad causes an undesirable phenomenon such that the leading end of a sheet engages the separation pad and is turned up.
In view of the foregoing problems involved in conventional techniques, it is an object of the present invention to provide a paper feed apparatus which has an improved sheet separation performance, facilitates operation, and prevents occurrence of paper jam of a leading end of a sheet.
It is an another object of the present invention to provide a paper feed apparatus which has an improved sheet separation performance, facilitates operation, and prevents occurrence of upturn of a leading end of a sheet.
In order to achieve the above-described object, the present invention provides a paper feed apparatus comprising: a picking roller successively picking a plurality of sheets of paper stacked on the shooter from the bottom of the paper stack, transporting the sheets of paper to a standby position and having one or a plurality of circumferential grooves formed on it; a gate extending substantially perpendicular to a paper transport direction and forming a predetermined clearance between the gate and the picking roller; a separation pad disposed in sliding contact with the outer circumferential surface of the picking roller and adapted to draw inside a single sheet of paper at a time from the standby station; a picking arm driven to move to an upper position when sheets of paper are placed on the shooter, and to a lower position when the sheets of paper are fed in order to press the sheets of paper placed on the shooter toward the outer circumferential surface of the picking roller in an area in the vicinity of a paper supply opening; and a paper guide disposed above the picking roller and having an opening and a bridge portion extending across the opening and fitted in a circumferential groove formed in an axially center portion of the picking roller.
The present invention also provides a paper feed apparatus comprising: a picking roller successively picking a plurality of sheets of paper stacked on the shooter from the bottom of the paper stack and transporting the sheets of paper to a standby position; a gate extending substantially perpendicular to a paper transport direction and forming a predetermined clearance between the gate and the picking roller; a separation pad disposed in sliding contact with the outer circumferential surface of the picking roller and adapted to draw inside a single sheet of paper at a time from the standby station; a picking arm driven to move to an upper position when sheets of paper are placed on the shooter, and to a lower position when the sheets of paper are fed in order to press the sheets of paper placed on the shooter toward the outer circumferential surface of the picking roller in an area in the vicinity of a paper supply opening; a pressing arm formed of an elastic material and disposed in sliding contact with the picking roller; and guide arms disposed on the upstream side of the pressing arm with respect to the paper transport direction such that their tip ends are located in proximity to the picking roller.
The present invention further provides a paper feed apparatus comprising: a picking roller successively picking a plurality of sheets of paper stacked on the shooter from the bottom of the paper stack and transporting the sheets of paper to a standby position; a gate extending substantially perpendicular to a paper transport direction and forming a predetermined clearance between the gate and the picking roller; a separation pad disposed in sliding contact with the outer circumferential surface of the picking roller and adapted to draw inside a single. sheet of paper at a time from the standby station; a picking arm driven to move to an upper position when sheets of paper are placed on the shooter, and to a lower position when the sheets of paper are fed in order to press the sheets of paper placed on the shooter toward the outer circumferential surface of the picking roller in an area in the vicinity of a paper supply opening; and a guide sheet formed of a material having a coefficient of friction lower than that of the material constituting the separation pad, the guide sheet being disposed to cover a portion of the separation pad such that the guide sheet does not contact the picking roller, and such that the leading end of the sheet of paper can abut and slide along the guide sheet.
The present invention further provides a paper feed apparatus comprising: a picking roller successively picking a plurality of sheets of paper stacked on the shooter from the bottom of the paper stack and transporting the sheets of paper to a standby position; a gate extending substantially perpendicular to a paper transport direction and forming a predetermined clearance between the gate and the picking roller; a separation pad disposed in sliding contact with the outer circumferential surface of the picking roller and adapted to draw inside a single sheet of paper at a time from the standby station; a picking arm driven to move to an upper position when sheets of paper are placed on the shooter, and to a lower position when the sheets of paper are fed in order to press the sheets of paper placed on the shooter toward the outer circumferential surface of the picking roller in an area in the vicinity of a paper supply opening; and a guide member disposed between the gate and the separation pad with respect to the paper transport direction, a surface of the guide member having an inclination angle with respect to the paper transport direction smaller than that of a surface of the separation pad, and the guide member being provided integrally with the gate or a holding member supporting the separation pad such that the guide member does not contact the picking roller and such that the leading end of the sheet of paper can abut and slide along the guide member.